Microbial<i>N</i>-dealkylation of atrazine: Effect of exogeneous organic substrates and behaviour of the soil microflora

Abstract

It has been demonstrated that atrazine side-chain mineralisation could be substantially stimulated by addition of carbon-containing substrates such as cellulose, green manure, straw or sawdust in the presence of NH4+ nitrogen but poorly affected by amendments with glucose. Cellulose has the most beneficial effect. For that substrate it has been shown that (i) simultaneous application of the organic amendment and atrazine results in kinetics for side-chain dealkylation showing a lag phase which is reduced or even eliminated by preliminary incubation with the amendment, (ii) rate and extent of mineralisation of the ethylamino side chain are significantly accelerated by decreasing the C/N ratio of the amendment. By comparison, mineralisation of the isopropylamino side chain is not appreciably affected by a change in the value of the C/N ratio as far as atrazine is applied within a two- to three-week period following the organic treatment after which a small deficit in N supply has a definite beneficial effect on mineralisation. Cellulose and, to a lesser extent, straw induce a biphasic change in bacterial number with more numerous and/or active atrazine degraders being predominantly found in the later-developing bacterial community. The fungal microflora is relatively unaffected by all types of carbon substrates but glucose and, unexpectedly, by atrazine at high ratio of application. Activation of atrazine mineralisation seems to be a co-metabolic process which is kinetically controlled by the rate of release from polymerised C substrates of easily available and readily metabolisable low-molecular-weight co-substrates. Transient production of glucose as an end-product of cellulose depolymerisation might induce catabolic repression of dealkylation enzyme systems and be responsible for a lag in atrazine side-chain mineralisation. © 1998 Society of Chemical Industry